1. Technical Field
The invention concerns a method of producing an overhead contact wire for supplying power to electrically driven vehicles and which comprises a copper-clad steel wire and a copper wire that is metallically joined to the copper-clad steel wire.
2. Description of the Prior Art
An overhead contact wire comprising a copper-clad steel wire is known from EP-A-0298518. The cladding of this overhead contact wire makes up between 45 and 75% of the overhead contact wire's cross-section and is metallically joined to the steel wire.
To produce such an overhead contact wire a cold soft steel wire is peeled and dipped into a molten copper bath so that a copper coating congeals on the surface of the steel wire. The thus obtained wire is then rolled at a temperature between 750 and 850.degree. C. and the cross-section is reduced by 10 to 40%. These processes are repeated until the desired thickness of the copper cladding is attained.
This method is known under the name of "dip-forming" and is very time consuming and expensive. This overhead contact wire takes into account that over time the copper cladding will be abraded by the current collector, and that the current collector will then directly contact the steel wire.
A method of producing an overhead contact wire is known from DE-A-3403872, wherein a steel wire is clad with a copper ribbon in a continuous operation and is formed into a copper-clad steel wire by means of a rolling device. A wire made of a wear-resistant copper alloy is attached to the copper ribbon during the same rolling process. In subsequent operations, the combined element is formed into the desired cross-sectional profile by means of rolling or drawing at room temperature. In the operating mode, the wear-resistant copper alloy wire makes contact with the current collector. Both the copper-clad steel wire and the wear-resistant copper alloy wire take over the tension force, while the copper cladding and the wear-resistant copper alloy wire are used for the current conduction. Wear caused by the current collector must be anticipated in spite of the fact that a wear-resistant copper alloy is being used, so that in time the overhead contact wire loses both the cross-section that carries the current as well as the cross-section that takes over the tension force.
Beyond that the simultaneous combination of a steel wire, a copper ribbon and a copper alloy wire produces many problems. Measures to improve the quality must additionally be taken with the copper alloy wire in order to achieve the high wear resistance.
It is an object of the present invention to present a method for producing an overhead contact wire in which the area that contacts the current collector has a high-tensile core made of a high-tensile steel wire and the current is conducted by a copper wire.
The method for producing an overhead contact wire for supplying electrically driven vehicles, comprises the steps of:
a) heating a steel wire to a temperature about 950.degree. C.; PA1 b) joining first and second metal band sections to a surface of the steel wire by means of rolling at a temperature of about 950.degree. C. under protective gas atmosphere to produce a combined element; PA1 c) reducing the cross-section of the combined element by at least 20%; PA1 d) heating a copper wire to a temperature about 950.degree. C.; PA1 e) joining the heated copper wire to the reduced diameter combined element in the area covered by the first band section by rolling at about 950.degree. C. under protective gas to produce a prepared wire; and PA1 f) reducing the cross-section of the prepared wire to produce an overhead contact wire.
The wear caused by the current collector is significantly reduced due to the fact that the second metal band section for encasing the steel wire is made of a high-tensile copper alloy. The cross-section of the steel wire and its alloy are designed so that the higher tensile strength of the overhead contact wire required for higher traveling speeds is taken over by the steel wire. The copper wire is essentially used to conduct current and its cross-section must be selected accordingly.
The invention will be fully understood when reference is made to the following detailed description taken in conjunction with the accompanying drawing.